Smokeless powder and process of manufacturing same



Patented Au 29, 1933 OFFICE SMOKELESS POWDER AND PROCESS OF ACTURINGSAME John M. Skilling, Penns Grove, N. J., and Oliver J. Teeple, Jr.,Cragmere, Del., assignors to E. I. du Pont de Nemours & Company,Wilmington, Del., a Corporation of Delaware No Drawing. ApplicationFebruary 10, 1932 Serial No. 592,178

This invention relates to an improved process for the manufacture ofsmokeless propellent powders. While the invention is adapted to themanufacture of nitrocellulose propellent pow- 5 ders generally, it isapplicable particularly to the manufacture of such powders for smallarms, such for example as pistols, revolvers, rifles and shotguns.

Prior to the present invention propellent powders have been, made by arather wide variety of processes. For example, smokeless powders of theso-called dense type have usually been made by colloiding dehydratednitrocellulose, in whole or in part, with a mixture of ethyl ether andethyl alcohol, or with other volatile solvents, such, for example, asacetone, and either with or without the incorporation of non-volatilesolvents or plasticizers, and with or without the incorporation ofnitroglycerine. After mixing, it has been the practice to press thepowder into blocks, these blocks being subsequently pressed through diesso as to form the powder into rods, tubes, ribbons, strips, and thelike, or the mass has been passed through or between rolls to formsheets, which are then cut into smaller lengths or grains of varioussizes and shapes. These powder grains were then subjected to a solventrecovery treatment so as to reclaim the volatile solvents, such as etherand alcohol, and the like, and subsequently subjected to a dryingtreatment to reduce the residual volatile solvent to a low point. Thedried powder grains were then passed through a screen or sieve to removeimperfect grains and then finally blended and packed. It 35 has alsobeen the practice in some cases to surface treat the powder grains thusformed with deterrent materials or to glaze them with graphite so as tomake them burn more progressively.

It is well known that smokeless powders produced by the foregoingprocesses have a more or less definite web or burning thickness obtainedby mechanical means. This web thickness in the case of tubular grainswith one or more perforations is the average thickness of the walls ofthe the case of ribbons or films of powder, the web is the averagethickness of the same when dried. In the case of powder grains out verythin, the web may then be the thickness of the out after shrinkage.

Onthe other hand, powders of the so-called bulk type are usuallygranulated in stills or pans into more or less spherical grains ofvarying sizes which do not possess a definite web or burning thickness.This type of powder is usually more powder after drying; that is, aftershrinkage. In.

similar in type to those used for the manufacture 5 of black powder.After incorporation, the material is placed in large inclined pans whichrotate through a tank of hot water or in a steam bath. The heat from thebath causes the water to evapcrate slowly from the composition, and asthis takes place the powder grains of varying sizes and more or lessspherical in shape are formed as the material rolls across the inclinedpan. These powder grains are sieved to a more or less definite grainsize, dried and hardened by spray- (6 ,ing the surface with a mixture ofacetone and ethyl alcohol or some other suitable volatile solventmixture having a colloiding action on the nitrocellulose. This treatmentcauses the outer surface of the gainsto be colloided to a greater extentthan the inner parts of the grains. The finished powder, after drying,is sieved again between two sieves to give a more or less definite grainsize.

In still another process for the manufacture of bulk smokeless powders,the nitrocellulose together with deterrents or plasticizers are agitatedin water or in an aqueous solution of barium or potassium nitrate.During agitation there is added a water insoluble solvent mixture to thenitrocellulose. This solvent may consist of amyl acetate, butyl acetate,or other suitable solvents diluted with benzol or other suitablediluent. The solvent mixture being insoluble in water, is separated intoglobules by the-agitation, and these globules colloid a certain amountof nitrocellulose causing it to form into soft grains or pellets. Byapplying heat to the mass, which is usually contained in a still, theexcess volatile solvent is driven off leaving the powder in the form ofrela- 10o tively hard grains which are more or less spherical in form,and which are more or less colloided depending upon the character,quantity, strength,

etc. of the solvent and methods used. The powder grains thus formed aredried and sieved, after which they may or may not be further treated byany of the known methods familiar to manufacturers of smokeless powders.

- An object of our invention is the manufacture of an improvedpropellent powder having a more I partially colloid the nitrocelullosein the or less definite web thickness of predetermined dimensions. Afurther object of our invention is an improved process of producingpropellent pow ders.

According to one embodiment of our invention we prepare anitrocellulose-water mixture and presence of water and with the aid ofvolatile solvents for nitrocellulose which are substantially insolublein water. The wet mass is then subjected to the action of pressure, bymeans of rolls or otherwise, in order to further colloid and form'themass into sheets or flakes of predetermined thickness and consistency.The volatile solvents are then substantially all removed from the sotreated material, and the sheets or flakes are subsequently reduced tothe proper grain sizes suitable for loading purposes.

In the foregoing process we preferably remove the excess water presentin the mixture before the second step of colloiding and gelatinizing bymeans of pressure applied to the mixture. While we preferably pass thematerial through a set of rolls to accomplish this second colloiding andgelatinizing effect, various ways of accomplishing this may be used suchas kneading or churning the material. In any case considerable pressureshould be applied. One of the advantages accomplished in passing themixture through rolls is that therolls may be set to give apredeterminedweb thickness to the grains or flakes. The reduction of thematerial to proper grain size may be accomplished in various ways but wepreferably pass the, material in the presence of water through a cuttingmachine such as an attrition mill or a Jordan engine, or other similarapparatus. A further and more specific embodiment of our inventioncomprises preparing the nitrocellulosewater mixture byagitating thematerials together to form a slurry. Other ingredients, as desired,

such as solvents, stabilizers, inorganic salts, de-

I excess water.

'terrents, and/or plasticizers, may be added to the slurry duringagitation. The excess water is then removed from this slurry bypassing'the mass over a screen or otherwise. The slurry may be con-.veyed to a second screen for removing further amounts of water or thismay be done by means of a screw conveyor which further'presses out Thematerial isthen subjected to the desired pressure /to furthercolloid andgelatinize the mass. This may be done by passing the mass through rollsset to form the mass into sheets or flakes of predetermined thickness.The material may then be subjected to regulated heat treatment to removethe volatile solvent, and may be cut to the desired grain or flake size.Before the solvent is removed it maybe desirable in some instances tosubject the material to further agitation after leaving the rolls so asto break up the sheets and facilitate the removal of the solvents whenheat-is applied. A further and more specific embodiment of our inventionisgiven in the following illustration: We make a slurry of water, or ofa water solution of inorganic nitrates and/or carbonates, such forexample as potassium and/or barium, or the like, and nitrocellulose of aquality suitable for propellant powders, together with, if desired, anystabilizing material and also any deterrent or plasticizing materialsuch .is charcoal, starch,

parafilne oil, dinitrotoluol, dimethyldiphenylur'ea,diethyldiphenylurea, dibutylphthalate, and like compounds suitable forthis purpose. To this slurry we add, during agitation, a quantity ofvolatile solvent or solvent mixtures for the nitrothese with other waterinsoluble solvents. These solvents may or may not be diluted by theaddition of water insoluble diluents such as benzol, toluoLpetroleumspirits,and the like. The parafflrie oil, dinitrotoluol,dimethyldiphenylurea, etc., referred to in the foregoing may, ifdesirable, be dissolved in a solvent rather than mixed with thenitrocellulose and then added-to the slurry with the solvent mixture.After the addition of the solvent mixture the mass is agitated until itshows a tendency to gr'anulate due to the colloiding action of thesolvent mixture on the nitrocellulose.

At this point excess water is drained off and the partially colloidedmass of nitrocellulose composition, together with occluded water is thenpassed through one or more'sets of rolls. Before doing so however, wemay also pass the material through a mechanical straining machine suchas a rubber straining apparatus'which assists in the removal of theexcess water and at the same time aids in further colloiding thematerial. The pressure exerted by the rolls tends to further colloid orgelatinize the nitrocellulose. The extent of this rolling treatment canbe modified to some degree according to the character of the finishedpowder desired.' In the final passage of the material through therolls,tthe rolls are set to give a more or less definite andpredetermined thickness to the leaf-like masses or sheets of colloidedmaterial. No one thickness can be specified as this must be regulatedaccording to the characteristics of the guns or ammunition for which the110.

powder is being made. However, for powder for a specific purpose, acertain thickness is predetermined and this is controlled by the degreeof rolling and final setting of the rolls. The mate-, rial at this pointis relatively 'soft and rich in solvent. For this reason the soft sheetsor leaf-like .masses of powder, together with a quantity of water, aretransferred to a still and .the excess solvent is boiled off andrecovered. This operation is continued until the residual volatilesolvent left in the powder mass is less than approximately 1%. Thisoperation also has the effect of hardening the colloided composition.The resulting material is'cut toa suitable size by various means or byany suitable machine such as the Jordon env gine or an attrition mill,and is sieved to the desired grain size, after which it may be dried,glazed with graphite, orthe snrfaqe may be impregnated withdinitrotoluol, dimethyldiphenylurea or other suitable impregnatingmaterial by any of the well known methods used for this purpose. in thismanner we obtain a propellent powder possessing a rather definite web orburning thickness which together with the composition and subsequentsurface impregnating treatment may be regulated to give certain desiredballistics which will be readily understood by those skilled in the art.

Powder made according to our process of manufacture'is suitable for usein small arms suchas revolvers, pistols, rifles, and shotguns and forvarious purposes to which small arms powders are applicable. The powdermay also be made in larger granulations for use in military ordnance,such for example as howitzers, field guns, 'etc.

The resulting powder according to our invention, whilehavingsubstantially all of the advantages of both the bulk and dense type ofpowders, the process has very definite economic advantages, a principalone being in reduced cost of manufacture of powder having a definite webthickness. For example, the manufacture of pressed nitrocellulose andnitroglycerine powders involves the dehydration of the nitrocellulose,colloiding of the dehydrated material, pressing thecolloid after mixingthrough dies and conveying the strings to a cutting machine to be cutinto grains. All of these steps require excessive handling of thematerial. The costs of dehydrating, pressing, cutting and handling thepowder, together with high solvent losses, are relatively large. Thesecosts are materially reduced by pressing a wet colloid through rolls,which may be enclosed to reduce solvent losses, using a water insolublesolvent mixture which may be recovered by boiling the leaf-like massesin water and finally cutting up the hardened leaf-like masses. By ourprocess these operations can be carried out in the manner indicated,thus eliminating cost of handling of powder.

While various embodiments of our new process exist and may be practicedwithin the scope of our invention, itis to be understood that we do notintend to be limited in the foregoing description and illustrationsexcept as indicated in the following patent claims.

We claim:

1. The process of making propellent powders which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, removing theexcess water, further colloiding and gelatinizing the nitrocellulose by'mechanical means, and removing substantially all the solvent therefrom.

2. The process of making propellent powder which comprises preparing anitrocellulose-water mixture, incorporating therewith an inorganic salt,partially colloiding the nitrocellulose with a substantiallywater-insoluble volatile .solvent, removing the excess water, furthercolloiding and gelatinizing the nitrocellulose by mechanical means,removing substantially all the solvent therefrom, and reducing thematerial to predetermined grain or flake size.

3. The process of making propellent powder which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, in the presenceof a deterrent or plasticizer, removingthe excess water, furthercolloiding and gelatinizing the nitrocellulose by means of pressure,removing the solvent therefrom and reducing the material topredetermined grain or flake size. 4. The process of making propellentpowder which comprises preparing a nitrocellulose-water mixture,partially colloiding the nitrocellulosewith a substantiallywater-insoluble volatile solvent, removing the excess water, furthercolloiding and gelatinizing the nitrocellulose by mechanical means,forming the mass into sheets or flakes of predetermined thickness,removing substantially all the solvent therefrom, and reducing thematerial to predetermined grain or. flake size.

5. The process of making propellent powder which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, removing theexcess water, further colloiding and gelatinizing the nitrocellulose bymechanical means, forming the mass into sheets or flakes ofpredetermined thickness, agitating the material to break up the sheetsor flakes of material, removing substantially all the solvent therefrom,and reducing the material to predetermined grain or flake size.

6. The process of making propellent powder which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, in the presenceof an inorganic salt and a deterrent or plasticizer, removing the excesswater, and further colloiding and gelatinizing the nitrocellulose byforming the material into sheets or flakes, agitating the material tobreak up the sheets or flakes of material, heating the material toremove substantially all the volatile solvent therefrom, and reducingthe material to predetermined grain size.

. '7. The process of makingpropellent powder which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, in the presenceof a stabilizer, removing the excess water, and further colloiding andgelatinizing the nitrocellulose by forming the material into sheets orflakes, agitating the material to break up the sheets or flakes ofmaterial, heating the material to remove substantially all the solventtherefrom, and reducing the material to predetermined grain size.

8. The process of making propellent powder which comprises preparing anitrocellulose-water mixture, partially colloiding the nitrocellulosewith a substantially water-insoluble volatile solvent, removing theexcess water and further colloiding and gelatinizing the nitrocelluloseby passing the mass through rolls whereby the material is formed intosheets or flakes, heating the material to remove substantially all thevolatile solvent therefrom, and reducing the material to predeterminedgrain size.

9. The process of claim. 8 in which an inorganic salt is incorporatedwith the partially colloided nitrocellulose before the excess water inremoved.

10. The process of claim 8 in which a deterrent or plasticizer isincorporated with the partially colloided nitrocellulose before theexcess water is removed.

11. The process of claim 8 in which an inorganic salt and a deterrent orplasticizer is incorporated with the partially colloided nitrocellulosebefore the excess water is removed.

'12. The process of claim 8 in which the sheets or flakes are broken upbefore the volatile solvents are removed.

JOHN M. SELLING. OLIVER-J. TEEPLE, JR.

